We present a 4 × 4 antenna array receiver designed for real-time Direction of Arrival (DoA) estimation of radio frequency sources within the 700-2600 MHz range. Our device, called RadioVision, overlays detected radio source markers onto optical images captured by a video camera. It features a heterodyne receiver with a 70 MHz intermediate frequency bandwidth, 16 ADCs operating at 140 MSPS, and an FPGA for real-time FFT and linear algebra computations. We have implemented the 2D U-ESPRIT algorithm in the frequency domain using Polyphase Filter Banks (PFBs) and pipelined FFTs, which reduces the number of needed ADCs, simplifies the calibration process, and filters out unwanted frequency bands. Experiments conducted in both rural and urban environments demonstrated the system's effectiveness. We achieved a mean squared error for DoA estimation of 1.78° at 90 m and 3.79° at 180 m in rural areas, and approximately 5.76° in urban settings at 60 m. This work represents the first on-field performance report of modern DoA algorithms, such as the 2D U-ESPRIT.